SQLite-Utils 4.0 Released with Database Schema Migrations and Nested Transactions

The latest release, sqlite-utils 4.0, marks the 124th iteration of the project and the first major version update since November 2020. This significant release introduces three key features: database schema migrations, nested transactions via a new `db.atomic()` method, and support for compound foreign keys. Database migrations provide a structured approach to evolving SQLite database schemas over time, defining a sequence of changes and tracking their application. Migrations are written in Python files and leverage the `table.transform()` method for advanced schema alterations not directly supported by SQLite's `ALTER TABLE` statement. The system includes a `_sqlite_migrations` table to log applied changes, ensuring a clear history of database evolution. This migration functionality was previously available as a separate beta package, `sqlite-migrate`, and has now been integrated into the core `sqlite-utils` library for broader accessibility within the `sqlite-utils`/`Datasette`/`LLM` ecosystem. The release also enhances transaction handling with nested `db.atomic()` capabilities, improving the safety and manageability of database operations, especially during migrations. Furthermore, support for compound foreign keys has been integrated, addressing a previously identified breaking change that would have been difficult to introduce later. Other notable updates include the use of SQLite's `INSERT ... ON CONFLICT ... DO UPDATE SET` syntax for upserts, automatic detection of primary keys, and improved column type detection during CSV and TSV imports.